The present invention relates to an on-line character recognition system for recognizing characters input by handwriting, making use of a pen-based input device.
In many conventional on-line character recognition systems, the character recognition is performed by examining matches of input character patterns to reference character patterns prepared beforehand. Therefore, it is required for precise recognition that the direction of the input character patterns not be different from the direction of the reference character patterns. However, when the input character patterns are hand-written, especially making use of a small tablet of an electronic pocket book, for example, the input character patterns may often be written by being inclined against the input frame or the tablet, a factor which degrades recognition performance.
To overcome this problem, some devices for normalizing the direction of the inclined character patterns have been proposed, as disclosed in Japanese patent application laid open as a Provisional Publication No. 269265/'88 (hereafter called the first prior art) or Japanese patent application laid open as a Provisional Publication No. 337963/'94 (hereafter called the second prior art).
In the first prior art, a straight line 10, as illustrated in FIG. 6, is written by a user before the user begins to input characters for indicating his preferred pattern inclination to be hand-written. Along the straight line 10, the user writes an intended pattern 9 of a character `A`, for example. By normalizing the pattern direction, referring the inclination of the straight line 10, an on-line character recognition system of the first prior art performs the pattern matching of the intended pattern 9.
For indicating the preferred pattern inclination, a rotary switch 11 of FIG. 7 is also proposed in the first prior art. The user manipulates the rotary switch 11 according to the inclination of the handwritten pattern 9 instead of writing the straight line 10. The on-line character recognition system of the first prior art normalizes the pattern direction referring to the rotation angle of the rotary switch 11.
In the second prior art, which is intended to be applied when two or more users facing each other input handwriting characters using a single tablet, for example, the direction of an input pattern are discriminated according to where the input pattern is written in the tablet or by which stylus pen the input pattern is written, by preparing two or more stylus pens. For each input field, or each stylus pen, a character direction is preset and the coordinates of the input pattern are normalized according to the character direction. The character direction may be discriminated making use of information of a beginning point of character strings or an input mode designated by the user.
However, with the inclination normalization method of the first prior art, the user is forced to write the straight line 10 or to manipulate the rotary switch 11 for indicating the pattern direction, which is burdensome for the user.
According to the second prior art, the pattern inclination cannot be normalized but with the character direction preset for each input field of the stylus pen. Therefore, when the character pattern is written differently to the preset character direction, it may not be recognized correctly, which is the same when the character direction is discriminated making use of other information.